1H- and 13C-Nuclear Magnetic Resonance (NMR) is being used to characterize toxic fungal metabolites. New compounds whose structures were determined include two biologically active norditerpenoid ditaclones (trivial names wentilactone A and wentilactone B) from Aspergillus wentii; bis-8,8'(7-hydroxy-4-methoxy-5-methylcoumarin), trivial name orlandin, from Aspergillus niger; 3,7-dimethyl-8-hydroxy-6-methoxyisochroman from Penicillium steckii; aflatoxicol A and B, biological metabolites of aflatoxin B1; and 6-ethyl-5-hydroxy-3-hydroxymethyl-5,6,7,8-tetrahydrochromone.